IntroductionDifferent pollution sources that have been topics of recent interest include improper waste dumping, incidental accumulation, agricultural chemicals, abandoned industrial activities and atmospheric fallout, among the most cited.1In particular, for mining and industrial abandoned sites, prior to evaluating the recovery of the polluted area, an evaluation of the extent and distribution of contamination is required in order to identify the area to be treated and the type of treatment that should be considered based upon the observed pollution trends. In these sources, heavy metals, HMs, frequently are the main pollutants and their mobilization due to weathering of solid inorganic materials under exogenic conditions is favoured, leading to environmental chemical pollution.For risk assessment purposes, the HMs mobility and their related availability is of a primal importance since toxicity is directly related to such characteristics.2Moreover, as is well known, pseudototal HMs content does not provide real information on available amounts of HMs and it represents the worst possible situation, overestimating the real hazard. Consequently, there is a need for a methodology able to provide information about reactivity or mobility of pollutants. In this sense, sequential extraction schemes (SES), became a commonly used evaluative and informative tool by providing details on the distribution or partitioning of HMs in soils and sediments, which is directly related to the prediction of their mobility.1This methodology is based on the process known as fractionation,3where a sequential series of selective extractant reagents with an increasing extractant power is employed. The goal of this procedure is to selectively dissolve or solubilise the different solid phases or mineralogical fractions.4–6By this methodology, knowledge of how HMs partition among the various geochemical phases is obtained. Such knowledge allows for a better insight into the mechanisms of HMs retention and release involved in the process of migration and decontamination, thus providing an evaluation of availability, mobility or persistence.Two decades ago, Tessier proposed a five-step SES, which is still widely used,7often with modifications in order to fit better to the target sample.8,9SES have been widely used to assess the mobile fraction of different HMs of environmental impact and to evaluate the HMs distribution between the different phases of a variety of samples such as industrially contaminated soils,10–19river sediments,20–25sewage sludge,26–30etc. The wide variety of SES and the related lack of comparability between results, led to the harmonisation of SES under the auspices of the former Community Bureau of Reference (BCR), now Standards Measurements and Testing (SM&T), producing a certified reference material for a three-step SES.31–33The main drawbacks of SES have been identified as readsorption and redistribution of metals.34–37Also, SES applications have been mostly limited to low contamination sites. However, SES are still very useful to identify trace element partitioning into the various solid phases of soil and to determine labile fractions of trace elements in a verifiable manner. On the other hand, SES data can provide additional valuable knowledge by a proper exploratory data analysis of the experimental information. For instance, a systematic correlation of the different fractionation data, normally absent, would help the process characterization of a particular contaminated area.Taking into account the mentioned limitations, the present study has been addressed to reveal the potential of SES application to a highly polluted site in overcoming the indicated boundaries. In this context, the present investigation is concerned with the fractionation of the HMs As, Cd, Cu, Ni, Pb and Zn in soils of a ditch network system designed to confine, control and monitor flows of water at a former abandoned mining area at Salsigne (France). Although As has not been considered in the SM&T-SES reference materials and applications (except in a recent work),38we have analysed the As content in the different fractions because it is the main toxic contaminant of the target soils. We are aware of the limitations of such results on As for a possible contribution to risk evaluation due to its particular chemical behaviour as an oxoanion. In this sense, values can be taken as the minimum mobility of this element under the given conditions. Furthermore, to best characterize the polluted site, a correlation of sample content was carried out by multivariate statistical analysis of SES data including latent factors responsible for the data set structure and apportioning of pollutant sources. A comparison of the obtained data with current regulation limits has been carried out and can be of use for risk assessment purposes.